Suture materials are classified as either absorbable or nonabsorbable, and are considered to be absorbable if they disappear from the sewn tissue within a year after surgery. Most absorbable suture materials disappear within shorter periods. Absorbable suture materials are preferred for applications in which the sewn tissues after healing should hold together without suture reinforcement and in which a nonabsorbable suture may provide the possibility of an adverse bodily reaction over an extended period of time.
The most commonly used absorbable suture materials are lactide homopolymer, glycolide homopolymer, copolymers of lactide and glycolide, and chitin. These monofilament synthetic absorbable suture materials are generally stiff and, therefore, these synthetic absorbable sutures are usually employed in a braided, multifilament construction in order to obtain the desired flexibility and softness. Silk, nylon and polyester are also employed in a braided construction as nonabsorbable suture materials.
Whether absorbable or nonabsorbable, such multifilament sutures show a certain degree of undesirable roughness or grabbiness in what has been termed their "tie-down" performance, i.e., the ease and smoothness of sliding a knot down the suture into place. Therefore, in order to improve the sliding properties of the sutures, surface coatings have been employed.
Sutures coated with beeswax to improve the living tissue absorption rate of the sutures is disclosed in Japanese Patent Laid-Open No. 59-181160(1984). Sutures coated with lubricious copolymers which contain polyoxyethylene blocks and polyoxypropylene blocks in order to improve the tie-down properties are disclosed in Japanese Patent Publication No. 61-30586(1986) and in U.S. Pat. Nos. 4,047,533 and 4,043,344.
Comparison of coated sutures with uncoated sutures reveals that the coated sutures exhibit improved sliding properties to a certain degree, but the improvement and effectiveness is insufficient. In addition, because the surface coating directly contacts living tissue, a coating material which is safe and nontoxic has been sought.
An object of the present invention is to provide sutures having good tie-down properties.
Another object of the present invention is to provide sutures coated with safe and nontoxic coating materials.